Lymphocytes from surgical patients will be prepared pre- and postoperatively and the response of these cells to PHA tranformation compared as a function of type of anesthesia. Total yield of lymphocytes and proportion of T and B cells, judged by sheep erythrocyte rosette formation, will also be assayed. In vitro studies of halothane action on PHA-induced alteration of cellular cyclic-AMP will be studied in human lymphocytes.